In conventional, in Japanese Unexamined Patent Publication No. 2001-221666, the inventor of the present invention has proposed an area flow meter having a sensor which is precise, compact and inexpensive. The conventional area flow meter having the sensor is structured such that a float moving up and down on the basis of a flow rate is provided within the taper tube having a translucency, a fluid to be measured flows therein from an inflow port in a lower portion and flows toward an inflow port in an upper portion, and plural sets of image sensor units each constituted by an optical lens and an image sensor are arranged along a vertical direction in one side of the taper tube.